1. Field of the Invention
The present invention relates to the structure of a spindle motor in a disk drive and a method of assembling the disk drive, and particularly, to the structure of a spindle motor that is easy to assemble to form a magnetic disk drive serving as an external storage device of a computer and a method of assembling the magnetic disk drive.
2. Description of the Related Art
Disk drives such as magnetic disk drives are classified into low- and high-end drives. The low-end drives have an average storage capacity and performance and are inexpensive. The high-end drives have a large storage capacity and high operation speed but are expensive. The high-end drives rotate many magnetic disks at a high speed.
The high-end drives involve complicated manufacturing processes because they have many magnetic disks around a spindle and because heads mounted on a carriage must be inserted among the disks. It is desired to provide a high-end magnetic disk drive having a simple structure that is assembled through a small number of processes.
A conventional magnetic disk drive has magnetic disks serving as recording media, a spindle motor for turning the disks at a specified speed, heads for writing and reading data to and from the disks, an actuator for positioning the heads on the disks, and a base (housing) for supporting the spindle motor and actuator. The actuator consists of a carriage, which holds the heads, and a voice coil motor for driving the carriage. The voice coil motor consists of a stator fixed to the base and a rotor that is a part of the carriage.
The shapes of the base or housing of the disk drive are classified into flat and bathtub. A necessary condition for the flat base here is that the surface thereof for mounting a spindle motor and an actuator is flat. It is not necessary for the flat base to have a flat surface for mounting a printed circuit assembly. Methods of assembling the flat and bathtub disk drives will be explained.
The flat-base disk drive will be explained first. The shaft of a spindle motor is fixed to the flat base by pressure or by an adhesive agent. Magnetic disks are attached to a hub of the spindle motor. A stator of a voice coil motor is fixed to the base.
An actuator, which has a carriage with heads, is mounted on the base so that the heads may not interfere with the disks. A shaft hole of the carriage is aligned with a shaft hole of the base, and a rotary shaft is inserted into the shaft holes from under the base. The carriage is turned to sandwich each disk between the heads. At the same time, the rotor of the voice coil motor integral with the carriage is inserted into the stator.
A cover is fitted to the base with a gasket being placed between them. Upper rotary shafts of the carriage and the spindle motor are attached to the cover. The spindle motor rotates the magnetic disks, and the voice coil motor swings the carriage to position the heads on the disks.
The bathtub-base disk drive will be explained next. A spindle motor is provided with a flange in advance. The spindle motor has a hub to which magnetic disks are attached. A bathtub base has a hole for receiving the flange.
The spindle motor is suspended from a first support of a jig. An actuator is fabricated from a voice coil motor and a carriage having heads. The carriage is suspended from a second support of the jig so that the heads may not interfere with the disks. The carriage is turned to sandwich each disk between the heads.
The jig with the spindle motor and actuator is lowered onto the bathtub base so that the flange fits into the hole of the base. The flange is fixed to the hole, and the carriage is fixed to the base.
A cover is fitted to the base with a gasket placed between them. An upper rotary shaft of the spindle motor and an upper rotary shaft of the actuator are attached to the cover. The spindle motor rotates the magnetic disks, and the voice coil motor swings the carriage to position the heads on the disks.
As mentioned above, the flat base is provided with the spindle motor in advance. The magnetic disks are attached to the spindle motor, and the actuator is mounted on the base. Thereafter, the actuator is turned to sandwich each disk between the heads. Namely, the flat base needs a space for turning the actuator to set the heads in the disks. In other words, the base must be flat to turn the actuator, and bases of other shapes do not allow this assembling method. The flat base is inapplicable to support a spindle motor that turns many disks at a high speed. The flat base may be warped due to clamping during a servo track write operation. The flat base has low rigidity and a low resonance point to do not resonate with the vibration of the bearing balls of the spindle motor. This may cause an error in the servo track write operation.
On the other hand, the bathtub-base disk drive employs the spindle motor provided with the flange. Each magnetic disk on the spindle motor is sandwiched between the heads of the carriage outside the base. Thereafter, the spindle motor and carriage are mounted on the base. The bathtub base is stronger than the flat base. The bathtub base, however, has the large hole to receive the flange. Accordingly, a part of the base where the flange overlaps the base is thin to deteriorate the rigidity of the base. The spindle motor having the flange is structurally complicated to increase the cost thereof.